<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <script src="vue.js"></script>
</head>
<body>
<div id="app">
    <span v-if="seen">Now you see me</span>
</div>

<script>

    const app = new Vue({
        el: '#app',
        data: {
            seen: true
        }
    })

</script>

</body>
</html>
